From: Nate Eldredge <neldredge AT hmc DOT edu>
Newsgroups: comp.os.msdos.djgpp
Subject: Re: inline assembly and c struct
Date: 02 Feb 2001 16:48:25 -0800
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To: djgpp AT delorie DOT com
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"clusty" <clusty AT poland DOT com> writes:

> I want compiler to print y_offset in my piece of inline assembly code.
> In above example i will get y_offset in variable and i.e instead of writing
> 
> asm(...
>     mov <y_offset>(%%eax),%%edx
>     ...)
> 
> I would have to write
> 
> asm(...
>     mov _y_offset,%%eax
>     mov <y_offset>(%%eax),%%edx
>     ...)
> 
> see the difference
> 
> i tried something like this
> 
> asm(...
>    "%0(%%eax),%%edx  \n"
>     ...
>     ::"m"(*(&some_struct.member-&some_struct)) /*this thing gives*/
>                                                /*variable at offset of*/
>                                                /*offset of member */
>    );
> but it won't work

I think what you want is (untested)

asm("movl %0(%%eax),%%edx"
    :: "i" (offsetof(some_struct, member))
   );

The "i" constraint specifies that this operand is an immediate value,
and hence will be inserted as a constant.

Note that you should always use the standard `offsetof' macro instead
of trying to calculate the offseet yourself.

-- 

Nate Eldredge
neldredge AT hmc DOT edu